In general, an integrated circuit refers to an electrical circuit contained on a single monolithic chip containing active and passive circuit elements. Integrated circuits are fabricated by diffusing and depositing successive layers of various materials in a preselected pattern on a substrate. The materials can include semiconductive materials such as silicon, conductive materials such as metals, and low dielectric materials such as silicon dioxide. Of particular significance, the semiconductive materials contained in integrated circuit chips are used to form almost all of the ordinary electronic circuit elements, such as resistors, capacitors, diodes, and transistors.
Integrated circuits are used in great quantities in electronic devices, such as digital computers, because of their small size, low power consumption, and high reliability. The complexity of integrated circuits range from simple logic gates and memory units to large arrays capable of complete video, audio and print data processing. Presently, however, there is a demand for integrated circuit chips to accomplish more tasks in a smaller space while having even lower operating voltage requirements.
As stated above, integrated circuit chips are manufactured by successively depositing layers of different materials on a substrate. Typically, the substrate is made from a thin slice or wafer of n-type or p-type silicon. The active and passive components of the integrated circuit are built within a thin n-type epitaxial layer on top of the substrate. The components of the integrated circuit can include layers of different conductive materials such as metals and semiconductive materials surrounded by low dielectric insulator materials. In attempting to improve integrated circuit chips, attention has been focused upon not only using different materials to construct the chips but also upon discovering new processes for depositing the various layers of materials on the substrate.
For instance, one area of circuit chip technology needing improvement is in the deposition of insulator materials used in the chips. Such an insulator material should have a very high resistivity, as low as possible dielectric constant, and sustainability of subsequent process steps and materials used in chip manufacturing. The low dielectric insulator materials are incorporated into integrated circuits in order to reduce power dissipation when the circuit is in use. If insulator materials with low dielectric constants (less than silicon dioxide) could be incorporated into integrated circuits, then the circuits would require less power and would simultaneously operate at higher speeds.
Currently, silicon dioxide is the most widely used electric insulator material. Silicon dioxide, however, which has a dielectric constant of about 3.84, is inadequate in meeting the stringent demands of proposed future fast, high performance and reliable low voltage devices.
Thus, those skilled in the art have been attempting to find a replacement to silicon dioxide for use in electronic circuits and other low voltage electronic devices. One alternative that has been suggested for use as an electric insulator in integrated circuits are amorphous fluoropolymers. For example, a fluoropolymer known as TEFLON AF marketed by EI DuPont de Nemours and Company has the lowest known dielectric constant of any plastic material. Unfortunately, problems have been experienced in attempting to deposit fluoropolymers on circuit chips. Not only has it been found difficult to form a film with good physical properties, but fluoropolymers do not readily adhere to substrates.
In the past, in order to form a film, fluoropolymers have been spin coated on substrates. According to this process, the substrate is first placed on a vacuum chuck and rotated at high speeds. A solution containing the fluoropolymer is then applied to the substrate. Due to centrifugal force, a coating is formed on the substrate which is dried and annealed on a hot plate or in a furnace. As described above, however, difficulties have been encountered with this process in getting the fluoropolymer to adhere to the substrate and in producing a film having good physical properties. Such deposition method usually generates course material with undesirable physical properties. Further, other problems have also been experienced in controlling various parameters, such as the thickness of the film.
In view of the above deficiencies of the prior art, a need exists for an insulating film that can be used as a replacement to silicon dioxide in electrical devices. A need also exists for a process for depositing various materials, such as insulators, on substrates for use in integrated circuit chips. In particular, a need exists for a process for depositing fluoropolymers on substrates, such as silicon, during the fabrication of integrated circuits.
In broader and more general terms, a need also exists for a new process for depositing a film or coating of a material on a substrate for use in any application, such as during the fabrication of integrated circuits.